When you are ready to cook, heat the BBQ and heat the oven to 200C/180C Fan/Gas Mark 4.
Spear the chicken with 2 metal skewers through the sides to keep it flat, and to make it easier to pick up.
Cut the onions and the lemons each into 6 wedges. Heat a deep roasting tray on the hob and add the oil.
Add the potatoes to the hot tray, rolling them in the hot oil to coat them. Add the onions and lemons and mix into the potatoes.
Season the whole lot with sea salt and milled pepper.